Tobacco composition

ABSTRACT

The concentration of polycyclic aromatic hydrocarbons in tobacco smoke is reduced by incorporating zinc oxide and a nitrate of a Group IIa and IIb metal into tobacco.

United States Patent [19] Norman et al.

[4 1 July 8,1975

1 TOBACCO COMPOSITION [73] Assignee: Liggett & Myers Incorporated,

Durham, NC.

22 Filed: Dec. 19,1973

21 Appl.No.:426,ll4

[52] US. Cl. 131/17 R; 131/265 [51] Int. Cl .1 A241) 15/02 [58] Field ofSearch l31/2,15,17, 140,141

[56] References Cited UNITED STATES PATENTS 2,429,567 10/1947 Sowa131/140 B 3,003,895 10/1961 Grunwald 131/17 R 3,251,368 5/1966 Neurath131/17 R 3,380,458 4/1968 Touey et a1. 131/17 R 3,720,214 3/1973 Nonnanet 131/17 R 3,807,416 4/1974 Hedge et a1 131/17 R FOREIGN PATENTS 0RAPPLICATlONS 3,794 9/1965 Netherlands 131/10 R OTHER PUBLICATIONSDangerous Properties of Industrial Materials," Text by N. lrving Sax,1251 pages, published by the Reinhold Book Corp., N.Y., Third Edition,1968, page $960 and 961, esp. cited.

Primary Examiner-Melvin D. Rein Attorney, Agent, or Firm-Kenyon & KenyonReilly Carr & Chapin [57] ABSTRACT The concentration of polycyclicaromatic hydrocarbons in tobacco smoke is reduced by incorporating zincoxide and a nitrate of a Group 11a and 11b metal into tobacco.

8 Clalms, No Drawings 1 TOBACCO COMPOSITION This invention relates to asmoking composition containin g tobacco and having a combination of acatalytic agent and an additive releasing nitric oxide associated withthe tobacco for reducing the concentration of polycyclic aromatichydrocarbons in tobacco smoke. More particularly it relates to suchcompositions wherein the catalytic agent is zinc oxide and the nitricoxide releasing additive is selected from the group consisting ofmagnesium, calcium and zinc nitrates.

BACKGROUND Observations of the mechanism of combustion in tobaccocompositions such as cigarettes, indicate that the smoke componentsresponsible for biological activity of smoke are formed in pyrolysiszone of the cigarette cone. It is widely accepted that much of thebiological activity observed in connection with cigarette smokecondensate resides in the neutral smoke fraction and more specificallywithin the subfraction which contains thee polycyclic aromatichydrocarbons (PCAl-l).

It has been generally accepted that it would be desirable to decreasethe levels of PCAH compounds in cigarette smoke and this has led to asubstantial amount of research aimed at reducing the proportion of suchcompounds in cigarette smoke.

It has been postulated that there are several pathways by which thetobacco components are converted into polycyclic aromatic hydrocarbons.One major route is the thermal degradation of various organic materialssuch as, e.g., cellulose into unsaturated free radical structuresconsisting of two, four or five carbon atoms and, in case of the longerfragments, of conjugated double bonds. The free radical structuressubsequently participate in the pyrogenesis of aromatic ring structures,the two and four carbon fragments giving rise to unsubstituted PCAl-land the five carbon branched structure giving rise to methyl substitutedPCAH. Another major route is the formation of PCAl-l from pre-extantskeletal structures already present in tobacco such as steroids. ln thelatter case only minor thermally induced modifications are necessary toproduce PCAl-l molecules. Many other routes, such as ring closures ofsidechains are possible.

Since the possible pathways of PCAH formation are widely different it ishighly unlikely that any one catalytic agent or other additive wouldinterfere with all of the different formation processes. For instance,in US Patent 3,720,214 there is disclosed a smoking compositioncomprising tobacco in association with finely divided zinc oxide. Thismaterial is disclosed to result in a tobacco composition wherein thepolycyclic aromatic hydrocarbon (PCAH) content arising from thepyrolytic reactions within this composition is substantially reducedwhen compared to a control cigarette. lt has now been found, however,that zinc oxide catalyst alone, while apparently very efficient ineliminating the production of PCAl-l by some of the pyrosyntheticroutes, has its limitations and does not affect all of the pathways.

The addition of nitrates and nitrites to tobacco has been previouslydescribed in various patents and publications. Thus French Pat. No.1,180,320 teaches the addition of unspecified amounts of nitrites totobacco and cigarette paper to reduce the PCAH yield and US. Pat. No.3,121,433 describes the addition of potassium nitrate to reconstitutedtobacco sheet to improve its burning characteristics. US. Pat. No.3,380,458 teaches the addition of 5.5 to 10% of potassium and sodiumnitrates to tobacco (NaNO 0.9l1.65% nitrate nitrogen, KNOg: 0.76-1.39%nitrate nitrogen) and it discloses a reduction in cigarette tar yieldwhich is caused by the concomitant increased burn rate of the cigarette.

Bentley and Burgan (Analyst 85, 727-730, 1960) describe the addition ofvarious nitrates to tobacco in an attempt to reduce the yield of3,4-benzopyrene. They achieved a reduction only with copper andpotassium nitrates and increases with lead, silver and zinc nitrates.

Wynder and Hoffman (Acta Pathol. Microbiol. Scand. 52, 119-132, 1961 andDeutch. Med. Wochenschr. 88, 623-628, 1963) using cigarettes treatedwith 5% copper nitrate (0.50% nitrate nitrogen) confirmed Bentley andBurgan's finding that copper nitrate reduced the 3,4-benzopyrene yieldof cigarettes. Hoffmann and Wynder also demonstrated (Cancer Res. 27,172-174, 1967) that the addition of 8.3% of sodium nitrate (1.37%nitrate nitrogen) resulted in a significant reduction of cigarette3,4-benzopyrene yield as well as in a reduction of the biologicalactivity of the smoke condensate. Pyriki et al. (Ber. Inst. Tabakforsch.Dresden, 12, 37-55, 1965), on the other hand, have shown that theaddition of 4% of potassium nitrate (0.55% nitrate nitrogen) increasedthe level of 3,4-benzopyrene in cigarette smoke by 40%.

While most of the past investigators have expressed their researchresults in terms of the effect of the additive on cigarette3,4-benzopyrene yield, it is now becoming widely recognized that thiscompound probably plays at most only a minor role in the biologicalactivity of tobacco smoke condensate. [t is also now recognized that theyield of 3,4-benzopyrene, which is a very minor constituent of the PCAHfraction, is not necessarily a reliable indicator of the additiveseffect on the bulk of the PCAl-l.

It has been postulated that the effect of nitrates on the composition ofcigarette smoke stems from two properties of nitrates: a) their capacityto oxidize, and b) their capacity to form the unpaired electron species,nitric oxide, in the pyrolysis zone of the cigarette that acts as a freeradical scavenger. Provided a sufficiently high level is added, allnitrates tend to lower the PCAH yield of cigarettes to some degree, butdepending on the particular cation, not necessarily the concentration ofPCAl-l in the smoke condensate.

The nitrates capacity to reduce PCAH concentration is particularlydependent on the ability of the salt to form nitric oxide in theappropriate temperature region of the combustion zone. Many of thenitrates and, in particular, nitrates of Group la metals are goodcombustion promoters. When they are added to tobacco the burn rate ofcigarettes is accelerated and the total smoke yield is decreased. Theconcentration of PCAH within the smoke condensate is, however, notnecessarily decreased and is at times increased. The nitric oxide yieldfrom such nitrates is relatively low. Hence, nitrates of Group la metalshave to be added at relatively high levels to reduce the concentrationof PCAH in tobacco smoke.

All added nitrates, and in particular those that accelerate burn rateimpart a disagreeable taste to the main stream smoke and an obnoxiousodor to the side stream aroma. For this reason, additive levels such ashave claimed to show beneficial effects in some of the previous work(5l0%) are unacceptable from the point of view of a palatable cigarette.In sum, nitrate, like zinc oxide, even though being an efficient agentfor disrupting some of the pathways of PCAH formation, has not proven tobe a universal elminator of PCAH. particularly at levels compatible withacceptable taste and smell of cigarette smoke.

DETAILED DESCRIPTION OF THE INVENTION In accordance with the presentinvention, the concentration of PCAl-l is substantially reduced withoutadverse organoleptic effect on tobacco smoke by incorporating both zincoxide and a Group lla or llb nitrate in tobacco. Unlike the Group lametal nitrates, the Group lla and llb metal nitrates do not acceleratecigarette burn rate. in addition they yield more nitric oxide per moleunder the conditions extant in the cigarette cone. Hence, they effectmore efficient reductions in the PCAH concentration in smoke condensate.

The incorporation of the nitrate compound enables reduction of the PCAHconcentration to levels below those achieved with zinc oxide alone. Thiseffect is achieved with nitrate concentrations well below the levelshaving objectionable effects on the organoleptic properties of smoke. inparticular, substantial reductions in PCAH concentrations are achievedat nitrate levels below 0.8% nitrate nitrogen, based upon the weight oftobacco.

The zinc oxide which has been found to be particularly effective incombination with tobacco to provide the smoking composition of thisinvention is A.C.S. grade zinc oxide which contains (on a weight basis)less than about 0.005% lead, 0.004% sulfate ion, 0.002% nitrate ion and0.001% chloride ion. The particle size of the zinc oxide is finer thanabout 50 US. mesh. Generally, the particle size is within the range of60-200 U.S. mesh with the greater portion of the material beingpreferably finer than 100 US. mesh.

The catalytic amount of zinc oxide associated with the tobacco in thesmoking composition is in the range of between about 0.1% to about byweight of the tobacco used to prepare the smoking composition. Althoughthe reduced yield of polycyclic compounds arising from pyrolyticreactions of the composition have been achieved at these levels, it hasbeen found that the best results are obtained when the zinc oxide is inthe preferred range of from about 0.5% to about 8% based upon the weightof the tobacco.

The nitrates which are employed in accordance with this invention arethe Group lla and llb metal nitrates, with calcium, magnesium, and zincnitrates being preferred. A nitrate which has been particularlyeffective in combination with zinc oxide and tobacco to provide thesmoking composition of this invention is A.C.S. grade Mg(NO )2.6H Owhich contains (on a weight basis) less than about 0.0005% chloride ion,0.005% sulfate ion and 0.004% heavy metals (calculated as lead).

As noted above, the proportion of nitrate associated with zinc oxide andtobacco in the smoking composition is below 0.8%, and preferably is inthe range of from about 0.25% to about 0.75%, calculated as nitratenitrogen. Although the amount of reduction of PCAH yield that is due tothe nitrate can be increased as the level of nitrate is increased, thetaste and aroma of smoke becomes progressively more obnoxious as thenitrate level is increased. Hence, in combination with 4 zinc oxide weprefer to operated in the 0.25 to 0.60% nitrate nitrogen range.

The additives should be well dispersed throughout the tobacco so thatthey will be uniformly effective during the entire period during whichthe composition is smoked. Furthermore, it is important to ensure thatthe dispersion effectively contacts a maximum volume of smoke which isinhaled by the user. Since the catalytic activity of the zinc oxide ismost likely a surface phenomenon, the greatest likelihood of maximumcontact between the smoke being drawn in by the user and the zinc oxideis obtained when the area/volume ratio of the zinc oxide particles ismaximized for a given weight of zinc oxide. For this reason, it isemployed as a fine powder of particle size, preferably smaller thanabout U.S. mesh.

The calcium, magnesium, and zinc nitrates are very soluble in water andcan be applied as a relatively concentrated solution which avoids theexcessive wetting of tobacco and yet assures good distributionthroughout the tobacco mass.

We have found that the combination of zinc oxide and nitrate compound ismost efficiently applied in a conventional casing solution of glycerinand propylene glycol wherein the zinc oxide crystals have been suspendedand by adding a sufficient amount of water to solubilize the requisiteamount of nitrate compound. Such a suspension-solution can beconveniently atomized on uncut tobacco strip by conventional casingapparatus.

Another method of application of the additives to the tobacco is to dryblend the zinc oxide, ground tobacco, a fibrous material and a binder.Dry blending, as in a conventional double cone blender effectivelydistributes the zinc oxide over the surface of the tobacco, includingthe pores within the tobacco surface which are large enough to acceptthe zinc oxide particles.

When required, dry blending is followed by wet mixing with water andcasing materials in proportions sufficient to provide the resultingmixture with the appropriate consistency for conventional reconstitutedtobacco sheet manufacturing operations. The sheet is then cut intostrips and a solution of nitrate compound in water is applied to thestrips. This is followed by a drying step if the tobacco moisture levelneeds to be adjusted. This material can be used in cigarette manufactureas such or it can be blended in any desired proportion with regulartobacco.

The fibrous material which is a constituent of the dry blend can be, forexample, oz-cellulose or fibrous tobacco stem material. The binderportion of the dry blend may be sodium carboxymethyl cellulose, or anatural gum such as guar gum. The casing materials used in the wetmixing step are usually glycerin and propylene glycol. Of course, anyother known fibrous material, binder of casing materials known to beuseful in combination with tobacco products can be used in combinationwith or in place of those herein set forth.

The weight proportions of the additives described above for use inreconstituted tobacco sheets are within the following approximate weightranges. The proportions shown are within the usual range required toprovide useful tobacco products.

Material Weight Fibrous 4-8 Binder l- Casing about 3-9 Comprising:

a) glycerin 4-4) h) propylene glycol 0.5-2 Tobacco balance to I001 Thesmoking composition may be further processed and formed into any desiredshape or used loosely e.g., cigars, cigarettes, and pipe tobacco in amanner wellknown to those skilled in the tobacco art.

The following Example is illustrative:

EXAMPLE 30.58 lbs. of ZnO and 28.52 lbs. of Mg(NO;,),'6l-l,O weresuspended and dissolved respectively in a mixture of glycerinpropyleneglycol casing solution and water and sprayed in a conventional casingapplicator onto 294 lbs. of uncut strip tobacco blend. The treatedtobacco was blended with 38.5 lbs. of reconstituted tobacco sheet and17.5 lbs. of stems. The resulting blend was cut at 32 cuts per inch.

Blends containing only the zinc oxide and only the magnesium nitrate aswell as a control blend containing neither additive were prepared in asimilar manner.

All four samples were pyrolyzed in a special pyrolysis reactorconsisting of a steel cylinder about 4 inches in diameter and 5 inchesalong with an annular space at the central perimeter covered with astainless steel screen. Cut tobacco was packed into this reactor atdensities similar to cigarette densities and the tobacco was lit at theexposed perimeter. The burning tobacco itself thus produced thenecessary heat for pyrolysis and the reactor closely approximated on alarge scale the conditions extant in a burning cigarette cone. Thecombustion and pyrolysis products were pumped out through a small tubepositioned concentrically with the cylinder and the dry solids in thesmoke were analyzed for PCAH content. The concentrations of PCAH in thetest tobaccos, as a per cent of the concentration of PCAH in the controltobacco are tabulated below for a typical run:

Concentration of Additive, wt.% PCAl-l Relative to Control Sample ZnOMg(NO Weight lR Analysis Basis 3 0.55 68 65 Control I00 As nitratenitrogen.

"From infrared spectral absorption in the region of aromatic C-l-ibonding vibrations. l l.9-l4.U a)

As is evident, Sample No. 3 illustrative of this invention, affordedmaterially lower concentrations of PCAH than were obtained with eitherzinc oxide or magnesium nitrate alone.

What is claimed is:

1. A smoking composition comprising:

a. tobacco;

b. finally divided zinc oxide in a catalytic amount of from about 0.1 toabout 15 weight percent sufficient to reduce the amount of polycyclicaromatic compounds in tobacco smoke; and

c. a nitrate of calcium, magnesium or zinc in an amount of from about0.25 to about 0.75 weight percent calculated as nitrate nitrogen. basedupon the weight of said tobacco, said amount being sufficient to effecta further reduction in the amount of polycylic aromatic compounds insaid smoke.

2. The composition of claim 1 wherein the concentration of zinc oxide isfrom about 0.5 to about 8 weight per cent and the concentration of saidnitrate is from about 0.25 to about 0.6 weight per cent calculated asnitrate nitrogen, based upon the weight of said tobacco.

3. The composition of claim 1 wherein said nitrate is magnesium nitrate.

4. The composition of claim 2 wherein said nitrate is magnesium nitrate.

5. A cigarette containing the tobacco composition of claim 1.

6. A cigar containing the tobacco composition of claim 1.

7. A pipe tobacco containing the composition of claim 1.

8. The process for making the composition of claim 1 comprising admixingcatalytic quantities of zinc oxide, said nitrate and tobacco to providea uniform dispersion of said zinc oxide and nitrate throughout saidtobacco.

1. A SMOKING COMPOSITION COMPRISING: A. TOBACCO, B. FINALLY DIVIDED ZINC OXIDE IN A CATALYTIC AMOUNT OF FROM ABOUT 0.1 TO ABOUT 15 WEIGHT PERCENT SUFFICIENT TO REDUCE THE AMOUNT OF POLYCYLIC COMPOUNDS IN TOBACCO SMOKE, AND C. A NITRATE OF CALCIUM, MAGNESIUM OR ZINC IN AN AMOUNT OF FROM ABOUT 0.25 TO ABOUT 0.75WEIGHT PERCENT CALCUATED AS NITRATE NITROGEN, BASED UPON THE WEIGHT OF SAID TOBACCO, SAID AMOUNT BEING SUFFICIENT TO EFFECT A FURTHER REDUCTION IN THE AMOUNT OF POLYCYLIC AROMATIC COMPOUNDS IN SAID SMOKE.
 2. The composition of claim 1 wherein the concentration of zinc oxide is from about 0.5 to about 8 weight per cent and the concentration of said nitrate is from about 0.25 to about 0.6 weight per cent calculated as nitrate nitrogen, based upon the weight of said tobacco.
 3. The composition of claim 1 wherein said nitrate is magnesium nitrate.
 4. The composition of claim 2 wherein said nitrate is magnesium nitrate.
 5. A cigarette containing the tobacco composition of claim
 1. 6. A cigar containing the tobacco composition of claim
 1. 7. A pipe tobacco containing the composition of claim
 1. 8. The process for making the composition of claim 1 comprising admixing catalytic quantities of zinc oxide, said nitrate and tobacco to provide a uniform dispersion of said zinc oxide and nitrate throughout said tobacco. 